Home |
Search |
Today's Posts |
#26
![]() |
|||
|
|||
![]()
On Sun, 7 Jan 2007 02:04:05 -0500, "Jimmie D"
wrote in : snip I must admit I never built a single transistor PA before SO I will have to look at the numbers again. Granted the push pull amp is more efficent than the single ended amp Not necessarily.... but Im still not sure about the gain. Il have to crank the #s when I dont have a snoot full of cold medicine. Please correct me if I am wrong but you are saying that two amps biased for say classB operation that a 2 transistor anp will have 6 db more output than a 1 transistor amp with the same drive power. No, just 3dB. Double your pleasure, double your fun. He probably does have an impedance matching problem , Yes he does. And his amp probably does, too. almost all amps of this type do to some degree. The impedance transformation of the transformers can almost always be improved upon by the inclusion of an adjustable L or Pi network in the output of the amp.. I know the last amp I tested had an output impedance of about 35 ohms. A matching network added to this amp increased power out, reduced harmonics and made the transistors stop popping. Impedance matching in an amp isn't a plug-n-play application. It's not as simple as reading the specs off the data sheet and punching numbers into a calculator. Since the big-signal gain of the transistors varies so much, each transistor pair much be physically measured, matched, and the impedance adjusted accordingly for maximum gain. The biggest problem with these amps is that the transformers have so few turns that they are very impedance-specific, as you discovered with your 35 ohm amp. There are only two solutions: either use transistors within a very narrow range of gain -or- change the gain (and therefore the impedance) of the transistors with negative feedback. I like the latter because it increases linearity. It does require each amp to be adjusted for any given pair of transistors, but almost all of the transistors in stock can be used because the gain range isn't nearly as limited. Yes, you can transform the impedance with a tuning network prior to the input transformer and after the output transformer, but it will limit the frequency response of the amp to a narrow bandwidth. This is how most of the so-called "broadband" CB amps are built. Most of the people who have used them know what a bitch it is to retune the amp every time you want to use it on a different part of the band. That's not "broadband" -- it's false advertising. |
Thread Tools | Search this Thread |
Display Modes | |
|
|
![]() |
||||
Thread | Forum | |||
Free speech | Antenna | |||
Free speech | Antenna | |||
AMATEUR'S USE AMATEUR AUXILIARY TO SUPPRESS FREE SPEECH | Policy | |||
Heil Clear Speech | Shortwave | |||
Heil "Clear Speech" DSP speaker | Shortwave |